1. Field of the Invention
The invention relates to urethanized xcex2-hydroxyalkylamide compounds, to a process for preparing them, to their use for preparing highly reactive powder coating materials, and to the powder coating materials themselves.
2. Description of the Background
Powder coating materials based on triglycidyl isocyanurate (TGIC) and acid functional polyesters give corrosion-resistant and weather-stable powder coatings. EP 0 536 085 describes, however, how the preparation of TGIC in solid form necessitates expensive processes or a relatively great, and therefore likewise expensive, purification effort. Moreover, TGIC is classified by the European Community as a category II mutagen (to be regarded as inducing heritable genetic defects) and as of May 31, 1998 has had to be labeled as toxic.
Toxicologically acceptable crosslinkers which are also more reactive include hydroxyalkylamides. In patents U.S. Pat. Nos. 4,076,917 and 4,101,606, the hydroxyalkylamides are combined with polymers having at least one carboxyl or anhydride function, in particular with polyacrylates, to form powder coating materials. EP 0 322 834 describes heat-curing powder coating materials which are composed of polyesters containing acid groups and of xcex2-hydroxyalkylamides. These coatings with xcex2-hydroxyalkylamide crosslinkers are highly weather-stable, very flexible, hard and chemical-resistant. For numerous applications, such as in the sanitation industry or in the coating of laboratory equipment, the chemical resistance is not, however, sufficient.
It was therefore the object of the present invention to find novel crosslinkers which in combination with carboxyl-containing polymers can be processed to powder coating materials which give coatings extremely resistant to chemicals.
It has surprisingly been found that urethanized xcex2-hydroxyalkylamide compounds constitute outstanding crosslinkers and, in combination with acidic polymers in powder coating materials, bring about a massively increased chemical resistance without detriment to the flexibility, hardness, reactivity, or weathering stability.
The present invention therefore provides urethanized xcex2-hydroxyalkylamide compounds synthesized from the components
A) from 65 to 96% by weight of xcex2-hydroxyalkylamide and
B) from 4 to 35% by weight of a nonaromatic polyisocyanate having an NCO functionalityxe2x89xa72,
the urethanized xcex2-hydroxyalkylamide compounds carrying hydroxyl groups terminally and having a functionalityxe2x89xa72.
The invention preferably provides urethanized xcex2-hydroxyalkylamide compounds wherein the xcex2-hydroxyalkylamide A) has the formula 
in which R1 is hydrogen or a C1-C5 alkyl group, R2 is hydrogen, a C1-C5 alkyl group or 
wherein R1 is as defined above, and A is a chemical bond or, a monovalent or polyvalent organic group selected from saturated, unsaturated and aromatic hydrocarbon groups, and substituted hydrocarbon groups, having 2 to 20 carbon atoms, m is 1 or 2, n is from 0 to 2 and m+n is at least 2.
With particular preference, these compounds of the invention have a functionality of four or more.
The invention further provides for the use of the urethanized xcex2-hydroxyalkylamide compounds to prepare transparent or pigmented, outdoor-resistant powder coating materials having high reactivity and hardness, excellent gloss and very good chemical resistance, prepared from the urethanized xcex2-hydroxyalkylamide compound and carboxyl-containing polymers and also from the adjuvants customary in the chemistry of powder coatings, such as pigments, fillers, leveling agents, devolatilizers, catalysts if desired, and other additives, for example.
The invention also provides transparent and pigmented powder coating materials comprising the urethanized xcex2-hydroxyalkylamide compounds of the invention.
The xcex2-hydroxyalkylamides A) are known in principle and are described, for example, in U.S. Pat. Nos. 4,076,917; 4,101,606; EP 0 322 834 and EP 0 473 380. The structure can be described as follows: 
in which R1 is hydrogen or C1-C5 alkyl, R2 is hydrogen, C1-C5 alkyl or 
where R1 is as defined above, and A is a chemical bond or a monovalent or polyvalent organic group derived from saturated, unsaturated or aromatic hydrocarbon groups, including substituted hydrocarbon groups of 2 to 20 carbon atoms, m is 1 or 2, n is from 0 to 2 and m+n is at least 2.
The nonaromatic polyisocyanate B) having an NCO functionalityxe2x89xa72 can be any aliphatic, (cyclo)aliphatic, cycloaliphatic or heterocyclic polyisocyanate having at least two isocyanate groups, or a mixture thereof. Polyisocyanates of this kind are mentioned, for example, in Houben-Weyl, Methoden der Organischen Chemie, Volume 14/2, page 61 ff. and in J. Liebigs Annalen der Chemie, Volume 562, pages 75 to 136. Representative examples of the polyisocyanates are aliphatic isocyanates such as alkylene isocyanates, e.g., ethylene diisocyanate, propylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, 2-methylpentamethylene 1,5-diisocyanate (MPDI), hexamethylene diisocyanate (HDI), trimethylhexamethylene 1,6-diisocyanate (TMDI), especially the 2,2,4 and the 2,4,4 isomer, and technical-grade mixtures of both isomers, decamethylene diisocyanate and dodecamethylene diisocyanate, and also cycloalkylene isocyanates, e.g. 1,3-cyclopentyl diisocyanate, 1,2-cyclohexyl diisocyanate, 1,4-cyclohexyl diisocyanate, xcfx89,xcfx89xe2x80x2-diisocyanato-1,4-methylcyclohexane, xcfx89,xcfx89xe2x80x2-diisocyanato-1,3-dimethylcyclohexane, 1-methyl-2,4-diisocyanatocyclohexane, 4,4xe2x80x2-methylenebis(cyclohexyl isocyanate), norbornane diisocyanate (NBDI) and 3,3,5-trimethyl-1-isocyanato-3-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI). Advantageous polyisocyanates are those obtainable by reacting polyisocyanates with themselves via isocyanate groups; especially isocyanurates, which come about through the reaction of three isocyanate groups. Mixtures of diisocyanates and isocyanurates, especially of 2-methylpentamethylene 1,5-diisocyanate, 2,2,4-trimethylhexamethylene 1,6-diisocyanate, 2,4,4-trimethylhexamethylene 1,6-diisocyanate, norbomane diisocyanate, isophorone diisocyanate, the isocyanurate of 2-methylpentamethylene 1,5-diisocyanate, the isocyanurate of hexamethylene diisocyanate or the isocyanurate of isophorone diisocyanate, are particularly advantageous. The polyisocyanates may likewise include biuret groups or allophanate groups.
The invention additionally provides a process for preparing urethanized hydroxyalkylamide compounds, which comprises reacting from 65 to 96% by weight of at least one xcex2-hydroxyalkylamide A) with from 4 to 35% by weight of at least one nonaromatic polyisocyanate B), the urethanized xcex2-hydroxyalkylamide compounds carrying hydroxyl groups terminally and having a functionalityxe2x89xa72.
The urethanized xcex2-hydroxyalkylamide compounds of the invention can be prepared in a solvent. Preferably, however, they are prepared in bulkxe2x80x94that is, without solvent. For this purpose, the xcex2-hydroxyalkylamide A) is introduced initially and the polyisocyanate B) is added. The reaction can be monitored by determining the NCO number and is over after from 30 minutes to 3 hours. Known methods and technologies are used for cooling, comminuting and bagging.
The present invention further provides for the use of the urethanized xcex2-hydroxyalkylamide compounds of the invention to prepare transparent or pigmented weathering-resistant powder coating materials of high reactivity and hardness and excellent gloss.
The invention additionally provides transparent or pigmented powder coating materials which comprise the urethanized xcex2-hydroxyalkylamide compounds of the invention and carboxyl-containing polymers and also the adjuvants customary in the chemistry of powder coatings, such as pigments, fillers, leveling agents, devolatilizers, catalysts if desired, and other additives, for example. In comparison to xcex2-hydroxyalkylamide crosslinkers containing no urethane groups, the coatings prepared from the powder coating materials of the invention are notable for a greatly improved chemical resistance.
Appropriate co-reactants for the urethanized xcex2-hydroxyalkylamide compounds of the invention, for the preparation of powder coating materials, are carboxyl-containing polymers. The polymers used can be addition polymers, polycondensates and polyaddition compounds. In principle, it is possible to use any polymer which contains at least two carboxyl groups and melts at at least 60xc2x0 C. For the purposes of the invention, particular preference is given to polycarboxyl polyesters and polycarboxyl polyacrylates.
The carboxyl-containing polymers are preferably polyester polycarboxylic acids which are prepared from polyols and polycarboxylic acids and/or derivatives thereof. The melting point of these acidic polyesters is situated within a range from 60 to 160xc2x0 C., preferably from 80 to 120xc2x0 C.; their acid number varies from 10 to 150 mg KOH/g, preferably from 30 to 60 mg KOH/g. The OH numbers should be below 10 mg KOH/g.
The polyester polycarboxylic acids to be used in accordance with the invention are prepared using polycarboxylic acids, such as, for example, oxalic acid, adipic acid, 2,2,4(2,4,4)-trimethyladipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid and pyromellitic acid. Examples of polyols used for the acidic polyesters are the following: ethylene glycol, 1,2- and 1,3-propanediol, 1,2-, 1,3-, 1,4- and 2,3-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,12-dodecanediol, 2,2,4(2,4,4)-trimethyl-1,6-hexanediol, trimethylolpropane, glycerol, pentaerythritol, 1,4-bishydroxylmethylcyclohexane, cyclohexane-1,4-diol, diethylene glycol, triethylene glycol and dipropylene glycol. It is of course also possible to react hydroxyl-containing polyesters, which are prepared by known processes from polycarboxylic acids and polyols, with polycarboxylic acids and/or polycarboxylic anhydrides to give the polyester polycarboxylic acids.
Suitable carboxyl-functional acrylate polymers possess an acid number of from 10 to 150 mg KOH/g and a melting point of from 60 to 160xc2x0 C. and are prepared by copolymerizing a monomer mixture consisting of
a) from 0 to 70 parts by weight of methyl (meth)acrylate,
b) from 0 to 60 parts by weight of (cyclo)alkyl esters of acrylic and/or methacrylic acid having 2 to 18 carbon atoms in the alkyl or cycloalkyl radical,
c) from 0 to 90 parts by weight of vinylaromatic compounds, and
d) from 0 to 60 parts by weight of olefinically unsaturated carboxylic acids, the sum of the parts by weight of components a) to d) being 100.
The monomers b) are preferably (cyclo)alkyl esters of acrylic or methacrylic acid having 2 to 18 carbon atoms in the (cyclo)alkyl radical. Examples of suitable, or preferably suitable, monomers b) are ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl methacrylate, neopentyl methacrylate, isobomyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate and stearyl methacrylate.
Examples of suitable monomers c) are styrene, vinyl toluene and ethyl styrene. Examples of d) are acrylic and methacrylic acid, which are also used with preference, and also crotonic acid, itaconic acid, fumaric acid, maleic acid, and citraconic acid.
The copolymers can be prepared by copolymerizing the exemplified monomers a) to d) by customary free-radical addition polymerization processes, such as, for example, solution, emulsion, bead or bulk polymerization.
The monomers are copolymerized at temperatures from 60 to 160xc2x0 C., preferably from 80 to 150xc2x0 C., in the presence of free-radical initiators and, if desired, of molecular weight regulators.
The carboxyl-functional acrylate copolymers are prepared in inert solvents. Examples of suitable solvents are aromatic compounds, such as benzene, toluene and xylene; esters, such as ethyl acetate, butyl acetate, hexyl acetate, heptyl acetate, methylglycol acetate, ethylglycol acetate, and methoxypropyl acetate; ethers, such as tetrahydrofuran, dioxane, and diethylene glycol dimethyl ether; ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl n-amyl ketone, and methyl isoamyl ketone; or any desired mixtures of such solvents.
The copolymers can be prepared continuously or batchwise. Normally, the monomer mixture and the initiator are metered continuously at a uniform rate into a polymerization reactor and at the same time the corresponding amount of polymer is taken off continuously. In this way, preferably, it is possible to prepare copolymers which are virtually uniform chemically. Chemically near-uniform copolymers can also be prepared by running the reaction mixture at constant rate into a stirred vessel, without taking off the polymer.
Alternatively, a portion of the monomers can be introduced as an initial charge, by way of example, in solvents of the stated type, and the remaining monomers and auxiliaries can be introduced, separately or together, into this initial charge at the reaction temperature. In general, the polymerization is conducted under atmospheric pressure but can also be carried out at pressures of up to 25 bar. The initiators are used in amounts of from 0.05 to 15% by weight, based on the total amount of the monomers.
Suitable initiators include customary free-radical initiators, examples being aliphatic azo compounds, such as azodiisobutyronitrile, azobis-2-methylvaleronitrile, 1,1xe2x80x2-azobis-1-cyclohexanenitrile and 2,2xe2x80x2-azobisisobutyric alkyl esters; symmetrical diacyl peroxides, such as acetyl, propionyl or butyryl peroxide, for example, bromo-, nitro-, methyl- or methoxy-substituted benzoyl peroxides, lauryl peroxides; symmetric peroxydicarbonates, e.g., tert-butyl perbenzoate; hydroperoxides, such as tert-butyl hydroperoxide, cumin hydroperoxide; and dialkyl peroxides, such as dicumyl peroxide, tert-butyl cumyl peroxide, or di-tert-butyl peroxide. To regulate the molecular weight of the copolymers it is possible to use customary regulators during the preparation. Examples that may be mentioned include mercaptopropionic acid, tert-dodecyl mercaptan, n-dodecyl mercaptan, and diisopropylxanthogen disulfide. The regulators can be added in amounts of from 0.1 to 10% by weight, based on the total amount of the monomers.
The copolymer solutions obtained from the copolymerization can then be supplied without further working up to the degassing or devolatilization process, in which the solvent is removed, for example, in a devolatilizing extruder or spray drier at from about 120 to 160xc2x0 C. under a vacuum of from 100 to 300 mbar and the copolymers to be used in accordance with the invention are obtained.
As polycarboxyl compounds, it is of course also possible to use mixtures of two or more substances.
The mixing proportion of the carboxyl-containing polymers and of the urethanized xcex2-hydroxyalkylamide compound of the invention is generally chosen such that the ratio of carboxyl groups to hydroxide groups is from 0.6:1 to 1.6:1.
It is normally not necessary to add a catalyst in order to increase the gelling rate of heat-curable powder coating materials. If the acidic polymer contains an aliphatic resin in which residues of 1,4-cyclohexanedicarboxylic acid (CHDA) and of the 2,2,4,4-tetramethyl-1,3-cyclobutanediol ester or residuces of 1,4-CHDA and of hydrogenated bisphenol A are present, then it is possible, as described in WO 95/01466, that catalysts comprising C1-C18 zinc, aluminum or titanium carboxylate salts, or aluminum oxides or zinc oxides, have an accelerating effect. They are used in amounts of from 0.03 to 1.0% by weight, based on the total amount of powder.
For the preparation of powder coating materials, the urethanized xcex2-hydroxyalkylamide compounds of the invention are mixed with the appropriate carboxyl-containing polymers and, if desired, catalysts and also pigments and customary auxiliaries such as fillers, devolatilizers and leveling agents. All of the ingredients of the powder coating material are homogenized in the melt. This can be done in suitable equipment, such as beatable compounders, for example, but preferably by extrusion, in the course of which the temperature ought not to exceed an upper limit of from 130 to 140xc2x0 C. After cooling to room temperature and appropriate comminution, the extruded mass is ground to give the ready-to-spray powder. The application of this powder to appropriate substrates can be done by the known techniques, such as, for example, by electrostatic or tribostatic powder spraying, unassisted fluidized-bed sintering, or electrostatic fluidized-bed sintering. Following the application of the powder, the coated workpieces are cured by heating for from 60 to 5 minutes at a temperature of from 150 to 220xc2x0 C.
Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.